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Friday, October 31, 2008

Polar warming 'caused by humans'

The rise in temperatures at Earth's poles has for the first time been attributed directly to human activities, according to a study.

The work, by an international team, is published in Nature Geoscience journal.

In 2007, the UN's climate change body presented strong scientific evidence the rise in average global temperature is mostly due to human activities.

This contradicted ideas that it was not a result of natural processes such as an increase in the Sun's intensity.

At the time, there was not sufficient evidence to say this for sure about the Arctic and Antarctic.

We really can't claim anymore that it's natural variations that are driving these very large changes

Peter Stott, Met Office

Now that gap in research has been plugged, according to scientists who carried out a detailed analysis of temperature variations at both poles.

Their study indicates that humans have indeed contributed to warming in both regions.

Researchers expected this result for the Arctic - because of the recent sharp increase in the melting of sea ice in the summer in the region - but temperature variations in the Antarctic have until now been harder to interpret.

Today's study, according to the researchers, suggests for the first time that there's a discernable human influence on both the Arctic and Antarctica.

Best fit

The research team took the temperature changes over the polar regions of the Earth and compared them with two sets of climate models.

One set assumed that there had been no human influence the other set assumed there had.

The best fit was with models that assumed that human activities including the burning of fossil fuels and depletion of ozone had played a part.

According to one of the researchers involved with the study, Peter Stott, head of climate monitoring and attribution at the Met Office, formally showing that the Antarctic was being influenced by human activities was the key development

"In the recent IPCC (Intergovernmental Panel on Climate Change) report for example," he said, "it wasn't possible to make a statement about the Antarctic because such a study had not been done at that point.

"But nevertheless when you do that you see a clear human fingerprint in the observed data. We really can't claim anymore that it's natural variations that are driving these very large changes that we are seeing in our in the climate system."

Professor Phil Jones, director of the Climate Research Unit at the University of East Anglia, said: "Our study is certainly closing a couple of gaps in the last IPCC report.

"But I still think that a number of people, including some politicians, are reluctant to accept the evidence or to do anything about it until we specifically come down to saying that one particular event was caused by humans like a serious flood somewhere or even a heatwave.

"Until we get down to smaller scale events in both time and space I still think there will be people doubting the evidence."